The present invention relates to apparatus and method for applying a viscous material. In particular, the present invention relates to apparatus and method for applying adhesive on an electric circuit substrate, such as circuit board bearing electronic components thereon.
FIG. 4 illustrates a conventional adhesive applicator (100) for applying adhesive onto the circuit substrate for holding components thereon. The applicator (100) has an application head (110) for applying adhesive on the circuit substrate, a robot (130) for moving the head (110), a substrate holder (140) for introducing the circuit substrate into an interior of the applicator and then holding the substrate, and a controller (150) for controlling overall operations of the applicator. The robot (130) moves the head (110) in the X-direction by means of a motor (132), and the holder (140) moves the circuit substrate in the Y-direction by means of another motor (142). As a result of relative movement between the head (110) in X-direction and the holder (140) in Y-direction perpendicular to the X-direction in a horizontal plane, the head (110) may apple adhesive on a predetermined area of the circuit substrate. The moving distance of the head (110) in X-direction and that of the holder (140) in Y-direction are controlled by the controller (150).
Referring to FIG. 5, there is shown the head (110). The head (110) is equipped with three sets of applying mechanisms or units (111) each of which squeezes out the adhesive with an aid of air pressure applied thereto. Each of the applying units (111) has a syringe (113) with a nozzle (112) for receiving the adhesive and then discharging a predetermined volume of the adhesive through the nozzle (112) with an aid of air pressure, an air-supply (115) for supplying compressed air to the syringe (113), and an elevator (120) for moving the syringe (113) up and down in the Z-direction shown in the drawing so as to apply the adhesive on a circuit substrate.
FIG. 6 shows several elements of the applying unit (111) in FIG. 5. As can be seen from the drawing, the air-supply (115) has a passage (116) for supplying the compressed air to the syringe (113), and a valve (117) for regulating an amount of compressed air to be supplied. The elevator (120) has a hollow shaft (121) connected to the syringe (113) and allowing the compressed air to pass therethrough, a lever (123) rotatably mounted on a support shaft (122), a cam follower (124) rotatably fixed to the lever (123), and a cam (125) making an engagement with the cam follower (124). One end (123a) of the lever (123) is connected to the elevation shaft (121), and the other end (123b) thereof may contact with the drive shaft of a nozzle-selection cylinder (126). The lever (123) driven by the nozzle-selection cylinder (126) causes the cam follower (124) to engage with the cam (125). This causes that the one end (123a) of the lever (123) rotates around the support shaft (122) in association with the rotation of the cam (125), moving the elevation shaft (121) up and down in Z-direction.
Referring to FIGS. 4-6, an operation of the applicator (100) so structured will be described in detail. The head (110) conducts a trial application of the adhesive (102) on a trial tape (101) before the application of adhesive onto a circuit substrate. As shown in FIG. 6, when the valve (117) of the air-supply (115) is opened for a predetermined period of time, the float (114) inside the syringe (113) is forced down due to the air pressure. This causes a predetermined volume of the adhesive (102) to be discharged from the syringe (113) through the tip end (112a) of its nozzle (112). The cam follower (124) of the lever (123) comes into contact with the cam (125) by the actuation of the nozzle-selection cylinder (126). As mentioned above, the rotation of the cam (125) causes the one end (123a) of the lever (123) to rotate, thereby the syringe (113) is moved down in the Z-direction via the elevation shaft (121). Then, the adhesive (102) discharged from the tip end (112a) of the nozzle (112) is applied on the trial tape (101) opposing to the nozzle tip end (112a). (see FIG. 5) After the application of the adhesive, the syringe (113) is moved up to the original position due to further rotation of the cam (125).
The condition of the applied adhesive (102) on the trial tape is imaged by a recognition camera (118) mounted on the head (110) (see FIG. 5). The controller (150) measures the area of She adhesive applied on the trial tape based on the output from the recognition camera (118), and determines whether the measured area meets a predetermined and intended diameter of the adhesive to be applied. The trial application of the adhesive followed by the image-pickup operation is repeated until the measured diameter of the applied adhesive on the trial tape falls within the allowable range of the intended diameter. After the diameter of the adhesive applied on the trial tape has come within the allowable intended diameter range, a circuit substrate is introduced into the apparatus and then firmly held by the holder (140). Then, the operation of applying the adhesive (102) onto the circuit substrate is started.
The prior-art applicator (100) has several drawbacks. For example, the volume of the discharged adhesive (102) varies depending on remaining amount of the adhesive (102) in the syringe (113), since the adhesive (102) in the syringe (113) is forced out by means of air pressure. U.S. Pat. No. 5,564,606 and JP (A)-276963/1999 disclose certain techniques for solving the problem of volume fluctuations of discharged viscous materials or adhesive.
Referring to FIGS. 7 and 8, the application mechanism (1) disclosed in JP (A)-276963/1999 mainly has an adhesive-applying member (4) equipped with a nozzle (3) for discharging adhesive (2), a discharge shaft (5) rotatably inserted in the hollow interior of the adhesive-applying member (4) and extending in the longitudinal direction along the axis of the nozzle (3), a driving device (6) for is rotating the discharge shaft (5) around its axis, and an adhesive supply unit (8) for supplying the adhesive (2) to the adhesive-applying member (4). A portion of the mechanism (1) surrounded by a circle indicated by alphabet I is illustrated in 9 in detail. As shown in the drawing, a screw-like portion (11) is formed at one end of the discharge shaft (5) close to the nozzle (3) (lower side of the drawing). Connected to the other end (5a) of the discharge shaft (5) (upper side of the drawing) is a transmission shaft (13) mounted for sliding along the axial direction relative to a connecting shaft (12) and for transmitting a rotation of the connecting shaft (12) to the discharge shaft (5). As shown in FIG. 7, an output shaft (7) of the driving device (6) is connected to the other end of the connecting shaft (12) via a coupling (14). Thus, when the driving device (6) is operated, the discharge shaft (5) is caused to rotate around its axis via the output shaft (7), the coupling (14), the connecting shaft (12) and the slidable transmission shaft (13).
With reference to FIG. 9, a passage (16) for supplying the adhesive is formed in the adhesive-applying member (4) at a position corresponding to the upper end (11a) of the screw-like portion (11). The passage (16) is communicated with a flexible adhesive-supplying tube (18) via a fixture (17). The flexible adhesive-supplying tube (18) is connected to the syringe (9) of the adhesive supply unit (8) (see FIG. 7) through which the adhesive (2) accumulated in the syringe (9) is supplied. When the discharge shaft (5) is rotated around its axis, the adhesive (2) supplied to the upper end (11a) of the screw-like portion (11) is forced toward the other end (11b) of the screw-like portion (11) along the thread groove formed on the screw-like portion (11). Since the adhesive-applying member (4) has the nozzle (3) arranged coaxially with the discharge shaft (5), the adhesive (2) moved to the other end (11b) of the screw-like portion (11) is then squeezed into the nozzle (3) and discharged from one end (3a) of the nozzle (3).
A nozzle stopper (19) is provided to the adhesive-applying member (4), adjacent to and parallel to the nozzle (3). The nozzle stopper (19) extends slightly longer than the nozzle (3) so as to define a small gap between the circuit substrate (20) and the tip end (3a) of the nozzle (3) when the tip end (19a) of the nozzle stopper (19) contacts with the circuit substrate (20) (see FIG. 7). This gap is advantageously used when a predetermined volume of the adhesive discharged from the one end (3a) of the nozzle (3) is applied as a mass of the adhesive having a predetermined diameter on a predetermined position of the circuit substrate (20). The nozzle (3), the adhesive-applying member (4) and the discharge shaft (5) are arranged so that they move altogether in the axial direction. In order to absorb a shock caused at the contact of the nozzle stopper (19) with the circuit substrate (20), a cushion spring (21) is provided to the adhesive-applying member (4).
The connecting shaft (12) is inserted into the interior of a hollow spline shaft (23) mounted for sliding along the axial direction and for rotation about the axis. Referring again to FIG. 7, a moving member (24) is provided around the outer peripheral surface of the end portion of the spline shaft (23) near the driving device (6) (upper side of the drawing). A component of a nozzle-moving device (30) is engaged with the moving member (24) for driving the spline shaft (23) upward and downward in the drawing. The stroke of this upward and downward motion is indicated by a distance between the imaginary line (35) (the upward position) and the solid line (36) (the downward position). In association with this upward and downward motion, the adhesive-applying member (4) moves up and down, so that the adhesive is applied on the circuit substrate (20) when the nozzle (3) formed on the adhesive-applying member (4) is moved downward.
A spline housing (25) is arranged around the outer peripheral surface at one end of the spline shaft (23) near the adhesive-applying member (4) (the lower side of the drawing). The spline housing (25) supports the spline shaft (23) slidably along the axial direction, and drives the spline shaft (23) to rotate together with the spline housing (25). For this driving, the spline housing (25) is supported by the frame body (29) of the applicator via a bearing (26). A pulley (27) is fixed to the spline housing (25), and this pulley (27) is driven by another pulley (37) of the rotation device (31) for the adhesive-applying member shown in FIG. 8 around the axis of the spline shaft (23) via a timing belt. The rotation of the pulley (27) rotates the spline housing (25) around its axis, and the rotation of the spline housing (25) rotates the spline shaft (23) around its axis in the same direction. Then, the rotation of the spline shaft (23) rotates the adhesive-applying member (4) connected to the spline shaft (23), and hence the nozzle (3) is rotated.
Referring back to FIG. 7, the supply unit (8) has the syringe (9) holding the adhesive (2) therein, the adhesive-supplying tube (18) for introducing the adhesive (2) held in the syringe (9) into the adhesive-applying member (4), and the compressed air-supplying device (32) for supplying compressed air into the syringe (9) so as to force the adhesive (2) accumulated in the syringe (9) into the adhesive-supplying tube (18). The compressed air is used for overcoming the viscosity of the adhesive (2) to feed the adhesive into the adhesive-applying member (4). Then, the adhesive (2) is discharged from the nozzle (3) due to the rotation of the screw-like portion (11) of the discharge shaft (5).
The adhesive-applying member (4) has a rotation-restricting structure (40) to which the adhesive-supplying tube (18) is connected. The adhesive-applying member (4) is mounted for rotation so as to rotate the nozzle (3) around the nozzle axis. If the adhesive-supplying tube (18) is directly connected to the adhesive-applying member (4), the adhesive-supplying tube (18) synchronously follows the rotation of the adhesive-applying member (4). The rotation-restricting structure (40) is provided to restrict rotation of the adhesive-supplying tube (18) even when the adhesive-applying member (4) rotates.
Referring again to FIG. 9, the rotation-restricting structure (40) has a main body (41) to which the adhesive-supplying tube (18) is connected so as to receive the adhesive (2), a locking cap (42) for fastening and locking the main body (41), a guide roller (43) mounted on the main body (41), and a spring (44) for biasing and positioning the rotation-restricting structure (40) in place. The guide roller (43) is fitted inside the guide groove (45) formed in the frame body (29) for blocking rotation of the rotation-restricting structure (40) even while the adhesive-applying member (4) rotates, preventing the rotation of the adhesive-supplying tube (18) connected to the main body (41). When the adhesive-applying member (4) moves up or down, the guide roller (43) slides inside the guide groove (45) so as to guide the upward or downward movement of the rotation-restricting structure (40). The spring (44) presses down the flange portion (46) formed on the adhesive-applying member (4) for firmly contacting the main body (41) onto the flange portion (46), preventing any leakage of the adhesive caused by the compressed air pressure.
The foregoing conventional applicator, however, has several drawbacks. First, the volume of the viscous material discharged from the nozzle varies depending on the remaining amount of viscous material within the syringe, as mentioned above. Even other applicator which has overcome this problem by forcing the viscous material out of the nozzle in association with the rotation of the screw-like portion has another disadvantage in that, volume of the viscous material discharged from the nozzle may also vary because of change of viscosity of the viscous material depending, for example, on a temperature change. Another technique has been disclosed in which the syringe is totally enclosed in an insulation material so as to avoid temperature change of the adhesive. However, the insulation increases the size of the equipment. Also, the insulation fails to meet the requirement unless it has a significant thickness.
Further, for another applicators, a rotation mechanism is provided for rotating the nozzle portion around the nozzle axis in order to change the application position of the viscous material by the use of nozzle having a plurality of openings, or in order to avoid an interference, for example, between the nozzle stopper and a wiring pattern formed on a circuit substrate. Such applicator is further provided with the rotation-restricting structure so as to prevent the rotation of the viscous material-supplying tube when the viscous material-applying member is rotated by the nozzle-rotation mechanism. As a result, the whole structure of the applicator becomes so complicated, which requires an extended maintenance. Furthermore, where the rotation mechanism for rotating the nozzle around the nozzle axis is provided to the applicator in which the viscous material is forced out by the screw-like portion, the rotation of the nozzle around the axis causes a relative rotation between the viscous material-applying member and the screw-like portion therein. This may result in that the viscous material between them is also forced out disadvantageously. The relative rotation may be eliminated by rotating the screw-like portion at the same angle/velocity synchronizing with the rotation of the nozzle, which requires a complicated, rotation-synchronizing control mechanism, for example.
Therefore, a purpose of the present invention is to provide an applicator capable of avoiding a viscosity change of a viscous material, such as an adhesive, which would otherwise cause due to a temperature change of the material. Further purpose of the present invention is to provide an applicator capable of achieving a nozzle-rotating system by using a simpler structure to thereby result in a simple structure, high cost-effective and less maintenance applicator.
Therefore, according to one aspect of the presnet invention, either or both of the nozzle and the substate are moved to determine relative positions thereof, and the nozzle is moved down to discharge and then apply a predetermined volume of the viscous material onto a predetermined position of the substrate. Also, the supply tube is connected to the application member so that the supply tube is rotated together with the application member.
In another aspect of the present invention, a thermal equipment is provided in the vicinity of the nozzle for keeping a temperature in the vicinity of the nozzle substantially at a predetermined value.
In another aspect of the present invention, a thermal equipment is provided in the vicinity of the nozzle or the inlet of the application member for keeping the temperature in the vicinity of the nozzle or the inlet of the application member for receiving the viscous material substantially at a predetermined value.
In another aspect of the present invention, a locking mechanism is provided for locking the application member into a hollow cylindrical spline shaft which is a member for holding and moving up and down the application member. The mechanism has a pair of J-shaped grooves each of which extends from one end of the spline shaft along an axial direction thereof, and a pair of pins each of which is fixed vertically to the application member for being inserted in each of the J-shaped grooves. Thereby, the locking mechanism locks the application member by inserting each of the pins into one end of each of the J-shaped grooves formed in the end portion of the spline shaft, sliding it along the J-shaped groove, and making it contact with the other end of the J-shaped groove.
A method for applying a viscous material of the present invention has discharging a predetermined volume of the viscous material from a nozzle to a predetermined position of a firmly held substrate for receiving the viscous material, and applying the viscous material on the predetermined position of the substrate. In particular, the viscosity of the viscous material is kept substantially constant by keeping the temperature in the vicinity of the nozzle substantially at a predetermined value to thereby stabilize the volume of the viscous material applied.